Michelle Wyer, HMRC's assistant director for the NMW, said letters had been sent to 102 labels that had exhibited at London Fashion Week in September.

"These letters give fashion houses plenty of warning that they are under scrutiny. If they are not playing by the rules, now is the time to put things right. Non-payment of the national minimum wage is not an option.

"Our message is clear: don't wait for us to come knocking on your door; put things right now and avoid a penalty and possible prosecution."